From the prospectus (March 2000 edition) entitled “Crane Construction Kit KBK classic and KBK ergo” of the firm Demag Cranes & Components GmbH, Wetter, Germany, there is known a crane construction kit system with c-shaped and I-shaped rails which are open at the bottom, by which one can implement different kinds of constructions, such as monorail telphers, or single and double-beam overhead cranes. In each case, the rails are suspended from support structures, other rails, or traversing gears which run into other rails. These suspension systems have a pendulum type design, which ensures that the rails align themselves and thus come into a state of equilibrium, i.e., no significant bending load occurs in the tension element. The pendulum suspension occurs through ball and socket bearings, having steel ball segments and mating ball cups with plastic slide shells. The ball segments are fastened to the end of a compound tension element. Thus, the tension element includes (looking down from above) a lug to fasten the tension element to the supporting structures, other rails or traversing gears, and a shaft joined to it as a single piece, to which the ball segment is screwed and secured.
In a suspension system of c-shaped rails open at the bottom, with a web broadening out toward the top and arranged at the top side of the rail, preferably a y-shaped or T-shaped web, the fixing device includes two identical fixing parts. These fixing parts are formed as sheet metal parts in such a way that, after being fitted together and held by screws, the broadening web of the rail is clamped in the lower region and the ball cup is accommodated in the upper region, while the tension element is passed through an opening.
This type of suspension system has been popular for many years and is easily installed on any given portion of a rail, since the fixing parts are fitted together there and tightened together by the screws for a clamping against the rail.
From U.S. Patent Publication No. 2004/0238473 A1 there is known a crane arrangement in which a bridge girder can run on parallel rails which are spaced apart from each other by means of traversing gears arranged at its ends. The bridge girder is clamped together with the traversing gears by u-shaped stirrups, open at the bottom, which enclose the bridge girder. Between the stirrups and the traversing gears there are vertically oriented ball and socket bearings, so that the traversing gears can turn 360 degrees about a vertical axis relative to the bridge girder and can also be tilted laterally. The ball and socket bearings used have balls made of steel and cups of nylon.
In these ball and socket elements, the ball of the tension element must be introduced into the ball cup, while the shaft passes through the central bore of the cup. Therefore, the tension elements are made of at least two parts, namely, a tension rod and a ball head, which are fastened to each other after being assembled with the tension rod introduced through the central bore in the ball cup. One often uses ball nuts that are screwed onto the tension rod. This connection is secured, for example, by a cotter pin.
The ball cups can be ruined by improper use or deficient maintenance. This results in increased friction between ball head and ball cup. In the case of two-part tension elements made from tension rod and ball head, the element securing the connection between tension rod and ball head is then overloaded. This can result in collapse of the bridge girder. The securing element can also fail, which likewise results in a failure of the suspension. Furthermore, the tension rod is weakened by the notch effect of the thread placed on it. Moreover, when the load is removed from the rail, the rail lifts slightly and the ball cup is pulled off from the ball head. When the rail is then placed under load, there is an abrupt loading of the ball and socket joint. This also has to be factored into the design.
Moreover, suspension systems are known from the firm Ingersoll Rand Zimmerman, of Milwaukee, Wis., for c-shaped crane rail open at the bottom, having a y-shaped web broadening at the top and arranged on the top side of the rail for a fixing unit made of two identical fixing parts. This suspension system has a tension element consisting essentially of a tension rod and a lug fastened thereto. The tension rod here is mounted in the lug by its lower end, able to turn about a vertical axis, and secured rigidly to a supporting structure at its upper end. The lug, in turn, is fastened by its bore to a bolt, extending in the lengthwise direction of the rail. Thus, the tension element can swivel transversely to the rail and can turn about a vertical axis. The tension element is rigid in and against the lengthwise direction of the rail. Furthermore, the bolt for the lug is mounted in the fixing parts. The fixing parts can swivel about the bolt and restrain a y-shaped web by means of screws. The screws for this are led through a borehole in the web.
Also known from the firm Krantechnik Müller, Lebach, Germany, are additional suspension systems for the above-described c-shaped crane rails, open at the bottom, with the y-shaped broadening web. These consist essentially of a two-piece tension element, two pivoting bearings, a bolt, a bracket and a fixing device. The tension element consists of an upper and lower piece, which are screwed together. The tension element has one borehole each at its upper and its lower end, each of which receive a pivoting bearing with a ball cup and a ball head. The lower ball head is connected to the bolt, which extends in the lengthwise direction of the rail. The ends of the bolt extending in front of and behind the ball head are each secured in pivoting manner and by a cotter pin in the legs of a u-shaped bracket, open at the top, whose web extending below and at a distance from the bolt is accommodated by the fixing device with the y-shaped web. For this, the fixing device in turn consists of two identical fixing parts, which are fastened by screws to clamp against the web of the bracket and the y-shaped web of the rail. The tension element again consists of multiple pieces.